Method of treating glass surfaces



Patented Sept. 26, 1944 METHOD OF TREATING GLASS SURFACES Frederick W.Adams, Pittsburgh, Pa., assignor to Pittsburgh Plate Glass Company,Allegheny County, Pa., a corporation of Pennsylvania Serial No. 477,447

No Drawing. Application February 1943,

1 Claim. (01. 41-42) The present invention relates to the formation ofmatte surfaces upon glass, and it has particular. relation to theformation of such surfaces by etching the glass with a corrosivesubstance, such as hydrofluoric acid.

One object of the invention is to provide a process of etching surfacesof glass to provide a matte a precipitant agent is added to the point ofincipient gelation. The solution is then subjected simultaneously toagitation and cooling until the plastic solution gels and breaks into afine susflnish, which is simple and inexpensive to practice,

and which produces a uniform and pleasing texture of the surface. I Ithas heretofore been proposed to form matte or dull finishes upon glasssurfaces by exposing them to the action of an etching agent, such ashydrofluoric acid. In thisoperation the entire surface is more or lessetched.

In accordance with the provisions of the present invention it isproposed to provide glass and notably structural glasses, such as thecoloured glass sold under the tradename of "Carrara glass, with a matteor dull finish in a stippled pat tern by applying to the surface asuspension in a non-solvent medium of very finely-divided plasticparticles designed to adhere to the surface in such manner as to provideminute points of protection and then to subject the surface to anetching agent, such as hydrofluoric acid, in order v to erode thoseportions of the surface not completely protected by the plastic.

In the practice of the invention various plastics which can be formedinto fine powders and which have reasonable resistance to the, etchingagentmay be employed. Vinyl resins such as partial polyvinyl acetalresins, e. g., polyvinyl butyral, which may be of the grade employed asthey reinforcing layer in safety glass is quite suitable for thepurpose. Still other resins that may be employed include vinyl chloride,vinyl acetate and the copolymer of polyvinyl acetate and polyvinylchloride known under the trade name of Vinylite H" which is understoodto include about 13% of polyvinyl acetate and about 87% of polyvinylchloride.- Acrylate resins, such as methyl methacrylate and butylmethacrylate, are'also contemplated. Cellu1osic esters, such ascellulose acetate, or cellulose ether, such as ethyl cellulose, maylikewise beemployed. xSimilarly heat hardenable plastics, such asalkydresins and "Bakelite resins in an intermediate stage ofpolymerization may be employed. I a

In the formation of a powder of the resin suitable for the practice ofthe invention any'method' which will yield finely-divided powders may beemployed. However, one of the most pract cal methods of forming suchpowder involves the solution of the plastic in asuitable solvent towhich pension of plastic particles in the liquid medium. This suspensionmay be drowned in additional precipitating agent and then filtered. Thefollowing constitutes specific examples of the preparation of powderssuitable for use in, the practice of the invention:

Example A About 150 parts of the resin obtained bypartial condensationof polyvinyl alcohol with butyraldehydewas dissolved in 850 parts ofsynthetic methanol. To this solution under agitation at room'temperaturewas added parts of water. The resin was partially precipitated duringthis addition but redissolved upon continued agitation to aclear fluidsolution. The chargewas continuously agitated and was gradually cooled.At 18 C. the charge became translucent and started gelling and at 5 C.the gel was quite heavy and viscous. Very strong agitation was requiredto keep the solution homogeneous at this point. At 3 C. some syneresisoccurred and at 10 C. the gel began breaking and precipitation started.At -20 C. the resin had precipitated and the product was in fluidsuspension. It was further cooled to 30 C. and an additional 2000 partsof water was added at this point to harden the resin. The. mixture waspoured into 3000 parts of water at room temperature and the product wasisolated by filtration. It was dried in a current of air at 25 C. toyield a very light fluffy powder, 94.7% of which readily passed a 200mesh sieve. Under the microscope the particle size appeared to be veryuniform and in the neighborhood of 1000 mesh. v

The filtered resin may be dried at any temperature below its softeningpoint without serious coalescence of the resultant powder. A temperatureof 45-50 C. has been found generally most satisfactory for polyvinylacetal resins.

Example B 1 A'solution was prepared by d ssolving under agitation atroom temperature, parts of the resin obtained by copolymerizing, 87parts of vinyl chloride and 13 parts of vinyl acetate in 900 parts -ofacetone. To this solution-under agitation were added 320 parts of 68%isopropanol. Particles of :resin precipitated during this addition butredis- 'in an oven at 65 0.-

had become very hazy and quite viscous. At 4' C. the resin precipitatedin very finely divided form to yield a fluid suspension. Cooling to 40"C. brought no further change in the appearance of the suspension.

An additional 700 parts of 88% isopropanol were added at 40 C. andimmediately thereafter 1500 parts of water raising the temperature to 24C. The charge was then dropped into 7000 parts of water at roomtemperature. After filtering and drying, less than 2% of the powderfailed to rpass a 200 mesh sieve.

Example 6' Fifty parts of a commercial polymerized methacrylic resinknown as Acryloid 130-27" were dissolved in 450 parts of acetone. Tothis solution under agitation at room temperature was subsequentlydried. It was then obtained g as a fine powder the majorportion of whichreadily passed a 200 mesh sieve.

Example D A sample of polyvinyl alcohol was prepared by the hydrolysisof low viscosity polyvinyl acetate by the method described by Blaikieand Crozier, J. Ind. and Eng. Chem. 28, 1158 (1936). According to thismethod 50 parts of the polyvinyl acetate known commercially as "VinyliteAYAA were dissolved in 100 parts of synthetic methanol. A solution of0.25ppart of caustic potash in 10 parts of methanol was added. Afterseveral hours, the solution had set to a gel and after 18 hours, arubbery gel remained covered by a clear mixture of methyl acetate andmethanol. The solvent was decanted and the gel was dissolved in water.The resulting solution was held at 90-100 0. until the residual methanoland methyl acetate had been distilled. Additional waterwas then added sothat the final concentration corresponded to the addition of 330 partsof water.

To this solution under agitation was added 330 parts of acetone byvolume. It was then chilled gradually to 10 C. where it gelled. At 20",the gel started synerizing and at the gel was definitely broken and theproduct had precipitated. At 25 to C. 1000 parts of acetone were addedand the resulting suspension was allowed to warm to room temperature andwas filtered. The filter cake was washed with 1000 parts of freshacetone and was then dried The product was thus obtained in dry lumpswhich were readily crushed under light pressure to afine powder. All but7% oi the product readily passed a 200 mesh sieve.

Ezample E Forty parts of a. commercial resin obtained by polymerizingethyl methacrylate were dissolved in a mixture consisting of 818 partsof 799. 5% alcohol and 60% parts of acetone by volume. The solutionagitated at room temperature and there was added a solutionconsistingof40partsotwaterin100partsoialco.

hol. The solution became slightly cloudy but no precipitation occurred.It was then gradually cooled. At 15 0.. the solution had becon quitecloudy and at 12 C. it began to gel. At 10 C. the gel started to breakand at 5' C. the eel had broken and there was a very fluid susl nsion.

The charge was cooled to 15 C. and w: there diluted with 140 parts oiwater. It wa' then poured with 2500 parts of water to form a linesuspension.

The suspension was filtered and the cake was washed with water. Itwasthen dried in an oven at 50 C. to form soft lumps which broke readilyinto a ilufly powder. liissentially all 01 the powder passed a 200 meshsieve.

The finely-divided or powdered plastic is suse pended in a suitablenon-solvent medium appropriate for the specific plastic. A small amountof asuitable plasticizer may also be added, in order to increase theadhesion of the plastic particles to the glass surface with which theycontact. The plasticirer preferably is soluble in the non-solventsuspension vehicle. A suitable system for cellulose acetate wouldcomprise a suspending medium selected from a class consisting'of mineralspirits, carbon tetrachloride. turpentine or the like. In such systemdimethyl phthalate or the phthalic acid ester of monomethyl ether ofethylene glycol may be added as a plasticizer.

For ethyl cellulose in powdered form a suitable system would compriseparaflln hydrocarbons, e. g., gasolene and dibutyl phthalate, tricres'ylphosphate or triglycol dihexoate as plasticizers.

For Bakelite resins in B state of polymerisation the system wouldcomprise mineral spirits or petroleum naphtha as suspension media anddibutyl phthalate as a plasticizer. Fbr partial polyvinyl butyral resinthe system would comprise petroleum naphtha or hydrogenated naphtha anddibutyl phthalate or trlethyleneglycol dihexoate, for the copolymer ofvinyl chloride and vinyl acetate a system might comprisetetrahydronaphthalene or butyl alcohol with dibutyl ph halate as aplasticizer.

system comprising finely-divided chlorinated rubber might consist ofpetroleum naphtha as a suspending medium and chlorinated diphenyl as theplasticizer.

' A system comprising methyl methacrylate resin in finely-divided formwould include mineral spirits as a suspension vehicle and dibuwlphthalate as the plasticizer.

The following constitutes specific examples 0! formulations which arecontemplated as being within the scope of the invention:

These formulations are merely exemplaryasit willbe thattheproportionsoitheplastic employed may vary over a relatively wide range. Of coursethe number of particles per unit area will vary in accordance with thetexture of the surface which it is desired. to produce.

This texture can be varied to some degree by increasing or decreasingthe proportion of plastic in the suspending medium or by increasing ordecreasing the thickness of'the coating applied to the glass surface. Byincreasing the proportion of plastic particles in the suspending mediuma greater number of particles are adhered to the glass surface, thusincreasing the protected area and decreasing the matte eflect. Bydecreasing the concentration of plastic particles in the suspensionmedium the area of glass exposed to etching is increased. The desiredeffect may be obtained by lightly stippling the surface with a spray ofthe suspended plastic, held at some little distance from the glass. Likeeffects might also be obtained by dipping the surfaces in a suspensionmedium containing only small amounts of suspended plastic and thenevaporating the medium. Care should be observed not to completely mashthe surface. a

The glass, after it has been sprayed, orotherwlaecoated',maybebakedatamoderatetemperature, e. g., 100 to 300 F.for a few minutes,

e. g., 5 to 15, in order to eiIect a more nearly complete union to theglass surface and also in the case of the heat hardenable resin, such as"Bakeli or alkyd resins to effect further polymerization in situ.

After the glass surfaces have been coated to the desired degree withplastic particles'and dried, they are exposed to etching, for example,with one or two normal hydrofluoric acid for a period dependent upon thedegree of etching which is desired. v The control of the etching actionis well understood in the art. Probably a period of about 5 or 10minutes will be satisfactory, though this period may be decreased oreven greatly extended if so desired. It will be apparent that the platesmay be etched with vapors of hydrofluoric acid in a closed chamber ifpreferred.

After the etching operation is completed the plates 'are subjected towashing to remove any excess acid. They may also be treated with asolvent for the plastic. in order to remove the adherent particles orthe particles may be removed mechanically by scraping. In some instancesit may also be desirable to heat the glass to a temperature sufllcientlyhigh to char the plastic particles and thus to facilitate their removalby scraping or brushing.

The forms of the invention herein disclosed are to be considered merelyas exemplary- It will beapparent to those skilled in the art thatnumer-- ous modifications may be made therein without departure from thespirit of the invention or scope of the appended claim.

What I claim is:

A process of providing a matte finish upon a glass surface whichcomprises coating the surface with a continuous liquid film comprising asuspension of fine solid organic plastic particles resistant to etchingacid in a volatile non-solvent liquid medium, evaporating the medium toleave the particles of plastic adherent in discrete state to the glasssurface, thereby providing dispersed points of protection upon saidsurface and then exposing the surface to the etching action of hydrogenfluoride to etch the unprotected parts of the surface.

' FREDERICK W; ADAMS.

